The invention relates generally to an earth moving device in the form of an elevating type scraper which has improved idler wheels for supporting and guiding the return runs of the elevator chain.
Large earth moving equipment of the scraper-elevator type is inherently noisy. It has not been generally recognized that a large portion of this noise is attributable to the hammering action of successive links of the elevator chain against the hard and inflexible surfaces of the steel idler wheels usually employed. Nor has it been generally recognized that aggravated wearing of the chain often experienced, particularly in the presence of abrasive materials handled by the scraper, is due to metallic contact at the idler.
Analysis shows that the reason for the hammering action is that the pitch of the chain, that is, the distance between adjacent pins is large as compared to the radius of the idler, indeed, in some designs approaching, or even exceeding the idler radius. Thus the chain instead of smoothly following the idler contour engages the idler in a series of abruptly angled chords. Because of this "chordal effect", each link causes the following one to be drawn with a large "lateral" velocity component against the surface of the idler which, at a high chain speed, releases a substantial energy of impact, resulting in the aforementioned noise and aggravated wear.
Since it is desired to retain a shallow apex angle for reasons of compact and efficient design, it is not possible to make the idler wheels of appreciably larger size.